1. Field of the Invention
The present invention relates to a battery having a terminal and a ceramic insulating sleeve.
2. Description of the Prior Art
FIG. 17 shows an example of a structure of a conventional ceramic hermetic seal for a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery comprises a winding type of elliptic-cylindrical electric power generating element 1, an elliptic-cylindrical metallic case 2 that houses the electric power generating element 1, and an elliptic lid plate 3 that is hermetically fixed to the metallic case 2 in such a manner that it is fitted into an upper opening of the metallic case 2 and welded thereto.
A positive terminal 4 and a negative terminal 5 connected to a positive electrode and a negative electrode, respectively, of the electric power generating element 1 each have a terminal supporting plate 7 attached thereto via an insulating sleeve 6 made of ceramic.
As shown in FIG. 18, the positive terminal 4 is hermetically fixed to the cylindrical insulating sleeve 6 in such a manner that it is inserted therein, and the corner formed by the positive electrode 4 and the upper surface of the insulating sleeve 6 is sealed with a brazing metal 8. In turn, the insulating sleeve 6 is hermetically fixed to the terminal supporting plate 7 in such a manner that it is inserted in an opening in the terminal supporting plate 7, and the gap therebetween is sealed with a brazing metal 10.
The positive terminal 4 is made of an aluminum alloy that is not dissolved in a non-aqueous electrolyte at a potential of the positive electrode. An aluminum or aluminum-alloy-based brazing metal 8 is used for brazing between the positive terminal 4 and the insulating sleeve 6, because the brazing metal will have the same potential as the positive terminal.
Since the terminal supporting plate 7 is insulated from the positive electrode, it may be made of an aluminum alloy, stainless steel, nickel-plated iron or the like. The brazing metal 10 between the terminal supporting plate 7 and the insulating sleeve 6 may be appropriately selected, not being limited to the aluminum or aluminum-alloy-based brazing metal.
On the other hand, as shown in FIG. 19, the negative terminal 5 is hermetically fixed to the cylindrical insulating sleeve 6 in such a manner that it is inserted therein, and the gap between the negative electrode 5 and the insulating sleeve 6 is sealed with a brazing metal 9. In turn, the insulating sleeve 6 is hermetically fixed to the terminal supporting plate 7 in such a manner that it is inserted in an opening in the terminal supporting plate 7, and the gap therebetween is sealed with the brazing metal 10.
The negative terminal 5 is made of a copper alloy, nickel alloy or the like, which is not susceptible to electrochemical corrosion at a potential of the negative electrode. A copper-alloy-based brazing metal 9, such as a gold-copper brazing, is used for brazing between the negative terminal 5 and the insulating sleeve 6, because the brazing metal will have the same potential as the negative terminal 5.
Since the terminal supporting plate 7 is insulated from the negative electrode, it may be made of an aluminum alloy, stainless steel, nickel-plated iron or the like. The brazing metal 10 between the terminal supporting plate 7 and the insulating sleeve 6 is the same as that of the positive terminal 4.
The terminal supporting plates 7 each having the positive terminal 4 or negative terminal 5 hermetically fixed thereto via the insulating sleeve 6 are hermetically fixed to the lid plate 3 in such a manner that they are inserted in openings at both ends of the lid plate and welded thereto. Then, the electric power generating element 1 mounted below the lid plate 3 is inserted in the metallic case 2, and the lid plate 3 is fitted into the upper opening of the metallic case 2 and welded thereto. In this way, the battery sheath is sealed.
The ceramic material used for the insulating sleeve 6 has a coefficient of thermal expansion that is extremely lower than that of the aluminum alloy used for the positive terminal 4, and is quite lower than that of the copper alloy used for the negative terminal 5.
Accordingly, a battery, such as a non-aqueous electrolyte secondary battery, having such a conventional ceramic hermetic seal structure has a problem in that a distortion may occur between the positive terminal 4 or negative terminal 5 and the insulating sleeve 6 due to a variation of temperature, and the distortion stress may be concentrated in the insulating sleeve 6 to cause a crack in the ceramic material, resulting in a degradation of air tightness of the battery sheath.
Thus, the positive terminal 4, which has a coefficient of thermal expansion especially largely different from that of the insulating sleeve, has been devised in terms of arrangement. That is, the brazing metal 8 is prevented from entering into the gap between the positive terminal 4 and the insulating sleeve 6 in order for the insulating sleeve 6 to be affected by expansion or shrinkage of the positive terminal 4 as little as possible, as shown in FIG. 18. However, such an arrangement could not completely prevent a crack from occurring in the ceramic insulating sleeve 6.
The stress of the distortion between the positive terminal 4 or negative terminal 5 and the insulating sleeve 6 may also be concentrated in the brazing metal 8 or 9 to cause a crack in the brazing material. A detailed research concerning why the crack occurs in the brazing material has proved that, when the brazing material applied to the terminal is cooled, a void is produced in the brazing material due to volumetric shrinkage of the brazing material, and the void causes occurrence of a crack.
If a crack exists in the brazing material, a problem may arise in that the crack develops to pierce through the brazing material, thereby degrading air tightness of the battery sheath. In such a case, there is an additional problem in that water is introduced into the battery and reacts with an active material (lithium if the battery is a lithium secondary battery, for example) to reduce the battery capacity or increase the internal resistance of the battery, which leads to decrease of the life of the battery.
The present invention has been devised to address such a circumstance. An object of the invention is to provide a battery having a terminal structure adapted to prevent an insulating sleeve or brazing metal from being damaged by a distortion caused by a difference in coefficient of thermal expansion between the metallic terminal and the insulating sleeve made of ceramic.
A battery according to the invention comprises: an insulating sleeve made of ceramic hermetically fixed into an opening in a battery sheath made of metal; a metallic terminal inserted in the insulating sleeve; and a metallic ring fitted over the metallic terminal. The metallic ring and the metallic terminal are hermetically fixed to each other by a brazing metal and the metallic ring and the insulating sleeve made of ceramic are hermetically fixed to each other by a brazing metal.
According to the arrangement, the metallic terminal and the insulating sleeve made of ceramic are fixed to each other via the metallic ring. Therefore, even if when the temperature varies, a dimension of the gap between the terminal and the insulating sleeve changes to cause a distortion due to the difference in coefficient of thermal expansion between metal and ceramic, the distortion can be accommodated by the metallic ring being deflected. Thus, a crack can be prevented from occurring in the insulating sleeve with reliability.
Preferably, the metallic ring is fixed to support the metallic terminal at an upper end face and/or lower end face of the insulating sleeve.
This can improve reliability of the terminal structure because the metallic ring also supports the metallic terminal, so that the metallic terminal is prevented from staggering.
Preferably, the metallic ring is fixed to the upper end face of the insulating sleeve that is exposed to the outside of the battery sheath.
This decreases the possibility that the brazing material is corroded, because the metallic ring is fixed to the outside of the battery sheath and the possibility that the brazing on the metallic ring is brought into contact with the electrolyte. As a result, the range of choices of the brazing material can be extended.
Preferably, a film made of a protective material having a corrosion resistance is formed on at least a surface of the metallic ring, the surface being exposed to the inside of the battery sheath, and/or at least a surface of the brazing metal for hermetically fixing the metallic ring, the surface being exposed to the inside of the battery sheath.
This arrangement can prevent the metallic ring or brazing metal at a potential of the positive or negative electrode from being corroded if it comes into contact with the electrolyte, because the surface of the metallic ring or brazing metal that is exposed to the inside of the battery sheath is covered with the film made of a protective material. As a result, the battery life can be prevented from decreasing due to a degraded air tightness. Here, the surface of only one of the metallic ring and the brazing metal which is inferior in corrosion resistance to the other may be covered with the film made of a protective material.
Preferably, a gap between the metallic terminal and the insulating sleeve is filled with a protective filler having a corrosion resistance, the gap being located to the inner side of the battery sheath compared to the parts of the metallic ring which is hermetically fixed to the metallic terminal and the insulating sleeve.
With this arrangement, since the protective filler is provided in the gap between the metallic terminal and the insulating sleeve, the metallic ring located on the outer side of the protective filler can be prevented from being brought in to contact with the electrolyte. Thus, the possibility that the metallic ring at the potential of the positive or negative electrode is corroded is eliminated, and the battery life can be prevented from decreasing due to a degraded air tightness. In addition, since the brazing metal for hermetically fixing the metallic ring to the metallic terminal and the insulating sleeve is not brought into contact with the electrolyte, the possibility that the brazing metal is corroded is also eliminated.
Preferably, at least a surface of the metallic ring that is exposed to the outside of the battery is covered with the brazing metal, so that the metallic ring is encapsulated in the brazing.
A research by the inventors has proved that voids (shrinkage cavities) are produced in the brazing material, not on the surface thereof.
This arrangement can suppress the void occurrence, because the metallic ring is disposed in the brazing where voids tend to occur and the brazing material is blocked from entering there.
Thus, the strength of the brazing is improved, and even when a distortion occurs due to a variation of temperature, a crack can be prevented from occurring in the brazing with reliability. When such an arrangement is applied to the brazing on the positive terminal, a significant effect of preventing crack occurrence can be provided.
Preferably, the metallic ring is a substantially right triangular in cross section.
In this case, the substantially-right-angled corner of the metallic ring conforms to the corner formed by the insulating sleeve and the metallic terminal protruding therefrom. In addition, since the outer surface of the metallic ring is inclined, the metallic ring can be placed without protruding.
Thus, the battery can have a more compact terminal structure.